My carpenter has suggested that rather than doing 2 layers of 5/8 sheetrock,
that I make the inner layer 3/4" OSB and then one layer of 5/8 sheetrock.
Does anyone have experience that suggests that I NOT to do this?

Only thing about plywood is that is can resonate to low-mid harmonics if
not muted.

sf

>My carpenter has suggested that rather than doing 2 layers of 5/8 sheetrock,
>that I make the inner layer 3/4" OSB and then one layer of 5/8 sheetrock.
>Does anyone have experience that suggests that I NOT to do this?
>
>Dave Martin
>DMA, Inc.
>Nashville, TN
>
>
>For more info, unsubscribe, large file uploads, ect: http://www.studiotips.com>Send small drawing files to dan@s...
>To Unsubscribe: Send email to
>acoustics-unsubscribe@e????ups.com

<< My carpenter has suggested that rather than doing 2 layers of 5/8
sheetrock,
that I make the inner layer 3/4" OSB and then one layer of 5/8 sheetrock.
Does anyone have experience that suggests that I NOT to do this? >>

Hey Dave:

Quite the contrary. I used 5/8"s drywall on RC on 5/8"s drywall on 1/2" OSB
on 1/2" foam board on scissor trusses with R-30 between trusses as my ceiling
design and it worked great (had to use styrofoam baffles netween trusses at
the truss ends to fit the R-30 in without choking the roof venting off)...
maybe an overkill desoign for you (I live next to the RR). As to the OSB ...
I felt it work out great ... reletively cheap stuff, high mass, and it let me
run wild (let the panel joints fall where they may) on subsequent layers
which saved a bit of cutting vs. having to follow the truss pattern for
locating joints. Also made for a very strong roof (scissor trusses are in
effect "decked" on both top and bottom with OSB).

Only thing about plywood is that is can resonate to low-mid harmonics if
not muted.
>>

S'truth

This is one of the reasons I put down a layer of foam board first on my
ceilings .. I hoped that the drywall OSB foam board sandwich would resist
vibration by being massive, composed of differential materials, and somewhat
cushoined from the roof trusses above by the foam board. I added RC and
another layer of drywall but might not be need for most folks ... I was
trying to keep RR noises outside.

I can still sometimes sense the trains, but I think the slab transmits more
sound than the ceiling ... which is saying a lot when you think about the
difference in mass of the two systems.

Well . . . let's not forget damping. People have, over
the years, made some fairly massive bells.

Back when I was doing research into the acoustics of
shells and membranes (shells are mathematically 3-di-
mensional, membranes 2-dimensional) I found that the
behavior depends primarily on the degree of mismatching
of characteristic impedances.

The characteristic impedance of air is fairly smooth,
but for low-damping membranes, it's dominated by
modal behavior. A membrane might very well be nearly
opaque and almost totally reflective at most frequencies,
and yet transparent at its natural modal frequencies.
(Let's remember that many loudspeaker cones that push
a *lot* of air, the highest intensity sound-locations
in a room, are made out of very thin sheets of paper
-- and yet they work.)

If you take a sheet of plywood or of gypsum and use it
on a wall, you're likely to have very low sound
transmission and very high reflection, except at a
few frequencies.

One of the ways to minimize this modal-frequency
transmission (which maps into what we might call "the
frequency response of a room") is to apply more damping.
Anything that converts panel vibration into heat will
tend to move that modal-panel characteristic impedance
away from the characteristic impedance of air.

Unfortunately, not many materials have high internal
damping. (Mathematically, the damping comes from the
imaginary part of the Young's Modulus of the material,
and -- working from memory here -- even that which we
call "high damping," such as lead, has an imaginary
part that's only about 5% of the real part.)

However, one thing that helps is to use dissimilar
materials as a laminate. One material might "ring
like a bell" at one frequency, another at a different
frequency. Where one is vibrating and the other is
not, we have a lot of relative motion. Something
that's even moderately energy-absorbing can convert
a lot of energy into heat when the relative motions
are exaggerated.

A laminate of gypsum and plywood or "particle board"
(both selected to have comparable -- but different
-- gross structural characteristics) with a mastic
in between, would probably work very well.
(Remember, though, that at low frequencies the
framework upon which the shells are layered is likely
to be the dominant factor -- at low frequencies,
mass is virtually insignificant, and you're left
with only bending stiffness.)

Aaahhhhh a relief! Someone with total sence! You go Richard!
One of the things I have found extremely effective in "layering", is
to use roofing felt in between layers of material. No matter what
kind of material(s) you use, it sharply increases efficiency.
Get the thickest type available, like AST 30. At about $10 a roll, its
very cheap. Most effective is to glue one site to the wood using
contact adhesive(one site only and do that outsite, or you'll get as
stoned as hell, followed by a huge headache...). Why does this work
so well? Roofing felt is paper, impregnated with bitumen. Bitumen is
one of the most effective damping compounds, especially good for low
frequencies.
For the same reason, a combination of a thick construction ply (4 or 5
ply, 3/4") and fire rated drywall is very effective. Ply is made by
gluing layers together under extreme heat, using a bitumen compound.
This combination (ply / drywall)is very effective over a much larger
frequency spectrum than 2 layers of the same drywall, especially in
the lower frequencies.
One of the most cost effective, "sandwiches" I've ever made consisted
of 3/4" ply, glued AST 30, 1/2" soundboard and fire rated drywall.

ROOFING FELT!! Sounds absolutely logical. I'm gonna try it on a gobo and
see. As soon as I get time. *S*

sf

>--- In acoustics@e????ups.com, richardplourde@m... wrote:
>> --- In acoustics@e????ups.com, Stephen Foster <oncourse@i...> wrote:
>> > Mass is mass. Mass is good. Mass is our friend.
>>
>> Well . . . let's not forget damping. People have, over
>> the years, made some fairly massive bells.
>
>
>Aaahhhhh a relief! Someone with total sence! You go Richard!
>One of the things I have found extremely effective in "layering", is
>to use roofing felt in between layers of material. No matter what
>kind of material(s) you use, it sharply increases efficiency.
>Get the thickest type available, like AST 30. At about $10 a roll, its
>very cheap. Most effective is to glue one site to the wood using
>contact adhesive(one site only and do that outsite, or you'll get as
>stoned as hell, followed by a huge headache...). Why does this work
>so well? Roofing felt is paper, impregnated with bitumen. Bitumen is
>one of the most effective damping compounds, especially good for low
>frequencies.
>For the same reason, a combination of a thick construction ply (4 or 5
>ply, 3/4") and fire rated drywall is very effective. Ply is made by
>gluing layers together under extreme heat, using a bitumen compound.
>This combination (ply / drywall)is very effective over a much larger
>frequency spectrum than 2 layers of the same drywall, especially in
>the lower frequencies.
>One of the most cost effective, "sandwiches" I've ever made consisted
>of 3/4" ply, glued AST 30, 1/2" soundboard and fire rated drywall.
>
>
>For more info, unsubscribe, large file uploads, ect: http://www.studiotips.com>Send small drawing files to dan@s...
>To Unsubscribe: Send email to
>acoustics-unsubscribe@e????ups.com

--- In acoustics@e????ups.com, Stephen Foster <oncourse@i...> wrote:
> ROOFING FELT!! Sounds absolutely logical. I'm gonna try it on a
gobo and
> see. As soon as I get time. *S*

Please be very careful with the adhesives you use. I
lost a friend who wasn't -- he was outside, using some
of those nasty adhesives to repair tiles in a swimming
pool. The fumes were heavier than air, collected at
the bottom of the pool where he was working. He passed
out, but didn't die -- he's now a vegetable.

Dear Koppert,
> ... This combination (ply/drywall) is very effective over a much larger
frequency spectrum than 2 layers of the same drywall,
especially in the lower frequencies. One of the most cost effective,
"sandwiches" I've ever made consisted of 3/4" ply, glued AST
30, 1/2" soundboard and fire rated drywall.... >
Where can I find measurement data about your statement ?
Also, what is "soundboard" and how do you apply it to AST 30 ?
Regards
Nestor
Mensagem original ------------------------------------------
De: Sjoerd Koppert [sjoerd@n...]
Enviada em: domingo, 7 de janeiro de 2001 16:16
Assunto: [acoustics] Re: OSB vs Gypsum?
In acoustics@e????ups.com , richardplourde@m... wrote:
>> Stephen Foster <oncourse@i...> wrote:
>> Mass is mass. Mass is good. Mass is our friend.
> Well . . . let's not forget damping. People have, over the years, made
some fairly massive bells.
Aaahhhhh a relief ! Someone with total sence ! You go Richard !
One of the things I have found extremely effective in "layering", is to use
roofing felt in between layers of material. No matter
what kind of material(s) you use, it sharply increases efficiency.
Get the thickest type available, like AST 30. At about $10 a roll, its very
cheap. Most effective is to glue one site to the
wood using contact adhesive (one site only and do that outsite, or you'll get
as stoned as hell, followed by a huge headache...).
Why does this work so well ? Roofing felt is paper, impregnated with bitumen.
Bitumen is one of the most effective damping
compounds, especially good for low frequencies.
For the same reason, a combination of a thick construction ply (4 or 5 ply,
3/4") and fire rated drywall is very effective. Ply
is made by gluing layers together under extreme heat, using a bitumen compound.
This combination (ply/drywall) is very effective
over a much larger frequency spectrum than 2 layers of the same drywall,
especially in the lower frequencies. One of the most cost
effective, "sandwiches" I've ever made consisted of 3/4" ply, glued AST 30,
1/2" soundboard and fire rated drywall.

On the subject of OSB, gypsum, layering, dampening, etc... I am
starting to build the outer "shell" of my room... I'm using 3/4" OSB
against the studs, then a layer of 1/2" homasote, then a layer of
1/2" sheetrock. I am hoping that the center layer of homasote will
act like roofing felt for a dampening effect between the OSB and
sheetrock. Any comments?

Ideally I would glue the homasote and sheetrock, but many of the
panels will be hanging upside-down, etc... I don't think there is any
adhesive that will hold a panel of gypsum to homasote and then the
homasote to OSB when upside-down. Even if there is, I would not
trust it for long term durability. The homasote would probably
separate. So, I will be screwing everything in. I realize that
screws will hurt the isolation effect, but I can't risk having panels
falling down. I'll just use a minimum amount of screws.

Remember that you need air between those layers. If you do
Gypsum-homasote-OSB with all of them glued together, you'll lose some of
the effect the homosote provides. As cheap as these felt/homasote layers
are, I'd do Gyp/homasote, air, and homasote/OSB. You'd need furring strips
in between, but that's cheap. Lots more bang for the buck.

Air is cheap. Air is our friend.

sf

>Hello,
>
>On the subject of OSB, gypsum, layering, dampening, etc... I am
>starting to build the outer "shell" of my room... I'm using 3/4" OSB
>against the studs, then a layer of 1/2" homasote, then a layer of
>1/2" sheetrock. I am hoping that the center layer of homasote will
>act like roofing felt for a dampening effect between the OSB and
>sheetrock. Any comments?
>
>Ideally I would glue the homasote and sheetrock, but many of the
>panels will be hanging upside-down, etc... I don't think there is any
>adhesive that will hold a panel of gypsum to homasote and then the
>homasote to OSB when upside-down. Even if there is, I would not
>trust it for long term durability. The homasote would probably
>separate. So, I will be screwing everything in. I realize that
>screws will hurt the isolation effect, but I can't risk having panels
>falling down. I'll just use a minimum amount of screws.
>
>Thanks - dm
>
>
>For more info, unsubscribe, large file uploads, ect: http://www.studiotips.com>Send small drawing files to dan@s...
>To Unsubscribe: Send email to
>acoustics-unsubscribe@e????ups.com

<< Remember that you need air between those layers. If you do
Gypsum-homasote-OSB with all of them glued together, you'll lose some of
the effect the homosote provides. As cheap as these felt/homasote layers
are, I'd do Gyp/homasote, air, and homasote/OSB. You'd need furring strips
in between, but that's cheap. Lots more bang for the buck.

Air is cheap. Air is our friend.

sf >>

Innit homasote already got the air in it? Not that more dead air is a bad
thing.

In any event, if you are going to furr it out, use resilient channel on the
last layer. RC is pretty cheap and works great (just look at STC specs for
walls with added RC layers).

As a disimilar damping layer, I'd reckon homasote works fine (that's what its
made for right?), but I used foam board as a damping layer in multi material
sandwiches (as opposed to homasote) and it worked great for me. The material
is fairly cheap, a breeze to work with (razor knifes much easier than
homasote or drywall and is light), and when it all gets screwed together
makes for a pretty dead sheathing structure ... just be sure to caulk it
before you cover it.

When we put my ceiling in (drywall on RC on drywall on foam board on OSB) the
train sounds from outside were pretty much gone after the 1st layer of
drywall went on the foam board ... I intuit that the roof framing got wiggled
quite a bit from trains shaking the ground, because the OSB (even after
caulking) still let in a good deal of sound ... but once we had a layer foam
bord, and then a layer of drywall up and caulked, things got real quiet. The
RC and last layer of drywall knocked it way down.

2. As a pin-up surface that can be painted or faced with fabric and has
mildly sound absorbing properties (compared to open face batt behind fabric
and wire) that can bring the ambient noise level down.

If you do not believe me, please go to http://www.homasote.com/ and review
mfr recommended uses. If you want to add a layer to a wall, I would spend
the money on something that is either heavier, stronger (gyp, plywood) or
fluffier (batt). Don't get me wrong, it's great stuff but more in
residential or commercial construction.